1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording for use to write data on a recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system in which the magnetization of signals is directed along the plane of a recording medium (the longitudinal direction), and a perpendicular magnetic recording system in which the magnetization of signals is directed perpendicular to the plane of a recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure in which a read head unit having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head unit having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head unit includes a coil and a main pole. The main pole has an end face located in a medium facing surface facing a recording medium. The coil produces a magnetic field corresponding to data to be written on the recording medium. The main pole passes a magnetic flux corresponding to the magnetic field produced by the coil, and produces a write magnetic field from its end face.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). An airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium causes the slider to slightly fly over the surface of the recording medium.
Here, the side of the positions closer to the leading end relative to a reference position will be referred to as the leading side, and the side of the positions closer to the trailing end relative to the reference position will be referred to as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs depending on the position of the magnetic head across the tracks.
Particularly, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing. In the present application, this phenomenon will be called unwanted erasure. The unwanted erasure includes adjacent track erasure (ATE) and wide-area track erasure (WATE). To achieve higher recording densities, it is necessary to prevent the occurrence of unwanted erasure.
A known technique for preventing unwanted erasure induced by a skew is to provide a wrap-around shield and a gap section, as disclosed in U.S. Pat. No. 8,472,139 B2, for example. The wrap-around shield is a write shield having an end face that is located in the medium facing surface and surrounds the end face of the main pole. The gap section separates the wrap-around shield from the main pole.
The wrap-around shield includes a leading shield, first and second side shields, and a trailing shield. The leading shield has an end face located in the medium facing surface at a position on the leading side of the end face of the main pole. The first and second side shields have two end faces located in the medium facing surface at positions on opposite sides of the end face of the main pole in the track width direction. The trailing shield has an end face located in the medium facing surface at a position on the trailing side of the end face of the main pole.
The gap section includes a leading gap section for separating the leading shield from the main pole, first and second side gap sections for separating the first and second side shields from the main pole, and a trailing gap section for separating the trailing shield from the main pole.
The wrap-around shield has the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, and thereby preventing the magnetic flux from reaching the recording medium. A magnetic head provided with the wrap-around shield is able to prevent unwanted erasure and provide further enhanced recording density.
The position of an end of a record bit to be recorded on the recording medium is determined by the position of the trailing-side edge (hereinafter referred to as the top edge) of the end face of the main pole in the medium facing surface. Accordingly, what are important for improving the write characteristics of the write head unit include: high write magnetic field strength at the top edge or in the vicinity thereof; and a large gradient of change in the write magnetic field strength at the top edge or in the vicinity thereof in the distribution of the write magnetic field strength in the direction in which the tracks extend.
As a structure of a trailing shield that can improve the write characteristics of the write head unit, U.S. Pat. No. 8,472,139 B2 discloses the following structure. The trailing shield includes a first portion located near the top edge of the main pole, and a second portion covering the first portion. The first portion is higher in saturation flux density than the second portion.
The trailing shield including the aforementioned first and second portions is formed by the following method, for example. First, a gap layer is formed on the main pole. Then, a magnetic layer made of a high saturation flux density material is formed on the gap layer. The magnetic layer is then patterned into the first portion by ion beam etching. This etching process performs over-etching to the leading shield. Then, a seed layer is formed to cover the first portion and the leading shield. The second portion is then formed by plating.
The magnetic head with the trailing shield including the aforementioned first and second portions suffers from the problem of unwanted erasure occurring due to the second portion. The reason therefor would be as follows. The second portion is formed on a non-flat underlayer. This causes the second portion to include a plurality of portions having different crystal growth directions. In such a case, the second portion has a greater number of grain boundaries and defects. In the second portion, magnetization rotation and domain wall displacement cannot smoothly proceed, and leakage magnetic field is thus likely to occur from the second portion toward the outside of the medium facing surface. This results in the problem of the occurrence of unwanted erasure.